Athletes accused of using performance-enhancing substances have long found refuge in four words: I've never tested positive. But that defense is being eroded. On Dec. 13 the Swiss-based Court of Arbitration for Sport (CAS) ruled that U.S. sprinters Tim Montgomery, the former 100-meter world-record holder and father of Marion Jones's two-year-old son, and two-time Olympian Chryste Gaines had committed doping offenses, even though neither had failed a drug test. Both were given two-year suspensions, and Montgomery's world mark of 9.78 seconds--broken in 2005--was expunged.

In its ruling CAS said it found "uncontroverted evidence of doping" by Montgomery, based on information from the BALCO investigation and the testimony of suspended sprinter Kelli White. White told the panel she discussed the steroid THG with Montgomery in 2001 at a meet in Portugal, and she also testified against Gaines.

This is not the first time an athlete has been punished for a "non-analytical positive." In 2005 U.S. sprinter Michelle Collins was banned for four years based on BALCO-related evidence. The Montgomery and Gaines cases further establish the powers of agencies like the United States Anti-Doping Agency, which prosecuted the cases, by allowing testimony from banned athletes.

Could the precedent be misused? "It's great to see the sport getting cleaned up," says Ato Boldon, a former sprinter from Trinidad and Tobago who won four Olympic medals. "But what if you have an athlete who, for purely malicious reasons, [testifies] against another?" Still, CAS endorsed aggressive prosecution, writing that even though "the conviction for doping offenses is more difficult when the evidence is other than positive testing," sports authorities should not be prevented from "using any available method of investigation."

This is not good news for four-time Olympic gold medalist Jones, who has been implicated by jailed BALCO founded Victor Conte and reportedly by former shot-putter C.J. Hunter, her ex-husband. (Montgomery said he and Jones have split up.) Travis Tygart, USADA's general counsel, told SI, "There are other active, BALCO-related cases, and we will continue to gather evidence in those cases." Jones has maintained her innocence and has never failed a drug test. But does that matter anymore?